This grant application proposes to study the organization of central nervous system pathways between the cortex, thalamus and basal ganglia in the adult cat, and the development of the laminar pattern of the corticostriatal projection in kittens. Several pathways will be studied with the autoradiographic and horseradish peroxidase methods: (1) the efferent and afferent connections of the intralaminar thalamic nuclei, (2) the efferent and afferent connections of the putamen, and (3) the efferent connections of the zona incerta and Fields of Forel. The fluorescent retrograde double labeling method will be used to study whether or not single neurons project doubly from the: (1) thalamus to both caudate nucleus and cortex, (2) cortex to both caudate nucleus and brainstem structures, and (3) globus pallidus to both centromedian-parafascicular complex (CM-Pf) and ventral anterior/ventral lateral complex (VA/VL), (4) caudate nucleus to both globus pallidus and substantia nigra, and (5) substantia nigra to both CM-Pf complex and VA/VL nuclei. The horseradish peroxidase and fluorescence methods will be used to study the development of the laminar origin of the corticostriatal projection in kittens during the first several postnatal days. In such studies, the data derived by the HRP method will be compared to the findings obtained by the more sensitive fluorescent method. Several hypotheses will guide the proposed research including: (1) that connectional studies on the intralaminar nuclei may have implications for understanding the putative functions of these nuclei, which include motor functions, modulation of sleep and wakefulness states, and modulation of noxious stimulation and analgesia, (2) that studies of the caudate nucleus, putamen and other basal ganglia may have clinical implications for understanding the mechanisms underlying Parkinson's and Alzheimer's Diseases, and (3) that the systems under investigation are replete with collateral axon connections, which may function in a variety of ways.